'\" et
.TH POSIX_FADVISE "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
posix_fadvise
\(em file advisory information
(\fBADVANCED REALTIME\fP)
.SH SYNOPSIS
.LP
.nf
#include <fcntl.h>
.P
int posix_fadvise(int \fIfd\fP, off_t \fIoffset\fP, off_t \fIlen\fP, int \fIadvice\fP);
.fi
.SH DESCRIPTION
The
\fIposix_fadvise\fR()
function shall advise the implementation on the expected behavior
of the application with respect to the data in the file associated with
the open file descriptor,
.IR fd ,
starting at
.IR offset
and continuing for
.IR len
bytes. The specified range need not currently exist in the file. If
.IR len
is zero, all data following
.IR offset
is specified. The implementation may use this information to optimize
handling of the specified data. The
\fIposix_fadvise\fR()
function shall have no effect on the semantics of other operations on
the specified data, although it may affect the performance of other
operations.
.P
The advice to be applied to the data is specified by the
.IR advice
parameter and may be one of the following values:
.IP POSIX_FADV_NORMAL 6
.br
Specifies that the application has no advice to give on its behavior
with respect to the specified data. It is the default characteristic if
no advice is given for an open file.
.IP POSIX_FADV_SEQUENTIAL 6
.br
Specifies that the application expects to access the specified data
sequentially from lower offsets to higher offsets.
.IP POSIX_FADV_RANDOM 6
.br
Specifies that the application expects to access the specified data in
a random order.
.IP POSIX_FADV_WILLNEED 6
.br
Specifies that the application expects to access the specified data in
the near future.
.IP POSIX_FADV_DONTNEED 6
.br
Specifies that the application expects that it will not access the
specified data in the near future.
.IP POSIX_FADV_NOREUSE 6
.br
Specifies that the application expects to access the specified data
once and then not reuse it thereafter.
.P
These values are defined in
.IR <fcntl.h> .
.SH "RETURN VALUE"
Upon successful completion,
\fIposix_fadvise\fR()
shall return zero; otherwise, an error number shall be returned to
indicate the error.
.SH ERRORS
The
\fIposix_fadvise\fR()
function shall fail if:
.TP
.BR EBADF
The
.IR fd
argument is not a valid file descriptor.
.TP
.BR EINVAL
The value of
.IR advice
is invalid, or the value of
.IR len
is less than zero.
.TP
.BR ESPIPE
The
.IR fd
argument is associated with a pipe or FIFO.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
The
\fIposix_fadvise\fR()
function is part of the Advisory Information option and need not be
provided on all implementations.
.SH RATIONALE
None.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIposix_madvise\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "\fB<fcntl.h>\fP"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
